A transmission comprising first, second and third parallel shafts and gearwheels which are carried by the shafts.
The present invention relates to a transmission, comprising first, second and third parallel shafts, rotatably supported in a casing, and gearwheels which are carried by the shafts and which intermesh with one another in pairs for transmitting torque either between the first shaft and the third shaft, or between the second shaft and the third shaft, and of which at least one gearwheel in each pair of intermeshing gearwheels is rotatably supported on its shaft and can be locked to or disengaged from its shaft by means of associated clutch members.
The use of transmissions of the type described above in vehicle gearboxes of having two concentrically supported input shafts, which can each be drive-connected to the output shaft of an internal combustion engine via its own disk clutch, is already known. In such a “power shift” gearbox the first and second shafts form two intermediate shafts, the third shaft usually forming the output shaft, to which torque is transmitted alternately via the one or the other intermediate shaft through alternating engagement of the disk clutches. When driving in a selected gear, the next gear is usually pre-selected by engagement of the relevant gearwheel on the currently non-driven intermediate shaft prior to the actual gearshift, so that the actual gearshift can, in principle, take place without interruption of the torque through simultaneous disengagement of the currently engaged disk clutch and engagement of the other disk clutch.
Such “power shift” gearboxes are often used in heavier trucks and plant vehicles and commonly have a total of ten or more gear ratios. The more gear ratios the gearbox is designed to have, the more gearwheels and clutches it requires and the more difficult it becomes to achieve suitable steps between the various gears in combination with an optimum span between the highest and the lowest gear ratio. A known method of minimizing the number of input shafts with associated clutch members is to have some or all gearwheels on the output shaft mesh with corresponding gearwheels on the two intermediate shafts. This means that the freedom to select steps between the various gears is more limited the greater the number of gearwheels on the intermediate shafts that mesh with common gearwheels on the output shaft. Maximum freedom, on the other hand, is obtained if each intermediate shaft gearwheel meshes with its own gearwheel on the output shaft, but this is then achieved at the expense of an increased number of requisite components.
It is desirable to provide a transmission of the type specified in the introductory part, which having few constituent components permits a large number of gear ratios with even steps between the gears.
According to an aspect of the present invention, at least two gearwheels rotatably supported on the first shaft and two gearwheels rotatably supported on the second shaft are coordinated by clutch members, which have neutral positions, in which both gearwheels are disengaged from their shaft and from one another, first engagement positions, in which the gearwheels are disengaged from the shaft but are coupled together for rotation together, and second engagement positions, in which one of the gearwheels is disengaged and one is locked to the shaft, and that the two gearwheels mesh with gearwheels on the third shaft in order to permit the transmission of torque from the first shaft via the third and the second shaft to the third, or from the second shaft via the third and the first shaft to the third shaft.
In a preferred embodiment of the transmission according to the invention three gearwheels are used on the first and the second shaft, the gearwheels being coordinated by clutch members, which have first engagement positions, in which either the first and the second or the second and the third gearwheel are disengaged from the associated shaft but are coupled together for rotation together.
By thus using three gearwheels with associated clutch members on the first and second shaft, it is possible, by way of a total of just eleven gearwheels, to transmit torque from the first or second shaft to the third shaft or vice-versa, with ten different gear ratios.